An optical sensor includes a function of, for example, sensing an object to be sensed or detecting a distance from the object to be sensed or the like, and an application field of such optical sensor has become wider.
An electronic device such as a mobile phone (including a smartphone) or a digital camera is provided with a liquid crystal panel for displaying an image thereon. Moreover, as such an electronic device, there is a model including a touch panel in order to allow a touch operation to be performed on the liquid crystal panel. For the electronic device including the liquid crystal panel and the touch panel in this manner, it is necessary to cause the touch panel to operate when performing a normal touch operation, but there is no necessity to cause the touch panel to operate when a face comes close thereto.
Accordingly, in order to reduce power consumption and prevent a malfunction of the touch panel, there is a growing demand for mounting, on the aforementioned electronic device, a proximity sensor so as to stop the operation of the touch panel when a face comes close to the liquid crystal panel. In response to such a demand, for example, in a mobile phone, in order to stop the operation of the touch panel during a call, a proximity sensor which senses that a face of a person comes close to the mobile phone is mounted on an audio output portion, which is put to an ear, of the mobile phone.
In addition, since an output value of a proximity sensor is inversely proportional to a proximity distance, there is a demand for using the proximity sensor as a range-finding sensor.
As an optical sensor that detects a position of an object, for example, PTL 1 describes that, by using a plurality of light-receiving elements, light from a light source is received, and a direction of the light source and a distance to the light source are detected to thereby sense a position of the light source.
Further, there is a demand for, by arranging a plurality of photodiodes in a light-receiving portion of an optical sensor, sensing a motion of an object from an amount of change in an output value of each of the photodiodes.
As an optical sensor that detects a motion of an object, for example, PTL 2 discloses a reflective optical sensor. As illustrated in FIG. 20, this optical sensor is provided with a light-emitting element 301 and two light-receiving elements 302 and 303, and the light-receiving elements 302 and 303 are respectively arranged on both sides of the light-emitting element 301. In a case where an object to be sensed 304 is on the right side, light reflected by the object to be sensed 304 strongly strikes the light-receiving element 303. On the other hand, in a case where the object to be sensed 304 is on the left side, light reflected by the object to be sensed 304 strongly strikes the light-receiving element 302. Thus, by reading a difference in photocurrents generated in the two light-receiving elements 302 and 303, it is possible to detect a position and a motion of the object to be sensed 304.
As to a sensor that detects a motion of an object, there is also a demand for using an optical sensor as a gesture sensor which senses a motion of a hand. Such a gesture sensor is used as an additional function of a proximity sensor, and senses a motion of a hand over a touch panel in a non-contact manner. Thereby, it is possible to perform an operation so as to scroll a screen displayed on a liquid crystal panel without causing a surface of the liquid crystal panel to be dirty even with a wet hand or a dirty hand.
PTL 3 describes a technique which enables sensing a moving direction of an object to be sensed with a sensor composed of one light-emitting element and a segmented photodiode. In a configuration described in PTL 3, metal layers are stacked on a four-segmented photodiode, and each of four light-receiving elements is caused to have directivity of sensitivity in four directions of up and down and right and left directions. By taking up-and-down differences and right-and-left differences as to signals from the four light-receiving elements, the moving direction of the object to be sensed may be specified.